In the field of automation technology, field devices presently are used which register and/or influence process variables. Examples of such field devices for registering process variables are fill level measuring devices, mass-flow meters, pressure meters, temperature meters, etc., which register the corresponding process variables fill level, mass flow rate, pressure, and temperature, respectively. Examples of field devices for influencing process variables are so-called “actors,” or actuators, which control e.g., as valves, the flow rate of a liquid in a section of piping, or, as pumps, the fill level of a medium in a container.
The field devices are connected via corresponding communications connections, normally via a data bus, with a process control center, which controls the entire course of the process, or which enables direct access to the individual field devices for operating, parameterizing, or configuring. By means of the direct access, settings (e.g. parameters) at the field device can be changed, or special diagnostic functions can be called-up. In addition to access via the process control center, temporary access, e.g. by means of a handheld device, portable computer, or cellular phone is possible.
In order to enable the operation of various field devices from the process control center, the functionality of a field device must be known to the process control center. The functionality of a field device is normally described using a device description. For this, special standardized device description languages are available; examples are CAN—EDS (Control Area Network—Electronic Data Sheet), Hart—DDL (Hart—Device Description Language), FF—DDL (Fieldbus Foundation—Device Description Language), Profibus—GSD (Profibus—Gerätestammdaten (Device Master Data)), Profibus—EDD (Profibus—Electronic Device Description). From the process control center, the operation of the field device is accomplished mostly by means of a graphical user interface, which facilitates start-up, maintenance, data protection, troubleshooting, and device documentation.
In the process control center, the measured values of the different process variables are evaluated or monitored, as the case may be, and the corresponding actuators are activated.
The transfer of data between the field device and the process control center is accomplished with wires, or wirelessly, in accordance with one of the known international standards for field busses, such as e.g. Hart, Foundation Fieldbus, Profibus, CAN, etc., or, for remotely arranged components of an installation, via public communication networks.
In the case of a process controlled from the process control center, which process is divided among several locations and includes a number of field devices, the amount of data to be transferred can lead to an overloading of the data bus system, or the public networks can be occupied too long, as the case may be.